Variable transmittance light filters, such as electrochromic light filters, have been proposed for many uses including in architectural windows; skylights; rearview mirrors, windows, and sunroofs for automobiles; and in certain imaging systems. Such electrochromic light filters respond to a change in applied voltage by changing their transmittance. In general, it has been a goal of designers of electrochromic elements to configure the elements to vary transmittance uniformly across the whole element.
As noted above, electrochromic elements have been employed as light filters in imaging systems such as cameras. Examples of cameras utilizing electrochromic light filters are disclosed in U.S. Pat. Nos. 5,555,069, 5,387,958, 4,554,587, and 4,256,372. In each of these patents, the electrochromic light filter is spaced apart from the image recorder (i.e., the film or image sensor array) and exhibits substantially uniform transmittance levels. Such electrochromic light filters are used in combination with the mechanical irises that are commonly used in cameras to vary the exposure level of the film or image sensor array. Such conventional mechanical irises are either hand operated or operated by a motor in response to the detected illumination of the scene or object to be imaged. Although the electrochromic light filters can vary the exposure level of the image recorder, a conventional mechanical iris is required if the camera is to allow for the depth of field of the image to be adjusted.
Integrated circuit optical sensors are increasingly used to provide visual input for control systems as well as in cameras. Many applications place optical sensors in harsh environments, requiring that the sensors be enclosed in a protective package. Presently, commercial optical sensor packages are developed from conventional semiconductor packages incorporating clear plastic or add-on windows to conventional molded or ceramic devices including a lead frame. An example of such a device is disclosed in U.S. Pat. No. 5,861,654. These packaging assemblies are expensive and difficult to manufacture.
An optical sensor may be used in applications exposing the sensor to a range of light intensities beyond the dynamic range of the sensor. As an example, a configuration allowing the sensor to operate at low light levels may cause the sensor to wash out at a high light level. As another example, consider a scene illuminated by fluorescent lighting, which cycles in intensity with the alternating current supply. A pixel array sensor with a high scan rate will have portions of each frame illuminated by varying levels of light. To avoid this problem, an integration period of at least approximately 30 milliseconds must be used. Since the scan time is generally a multiple of the integration time, a camera set to 30 milliseconds scan period for a bright scene may result in an excessively long scan time for a dim scene. Further, particularly if a lens is used to focus light on the sensor, direct exposure to sunlight can generate sufficient heat to damage sensor elements. Applications where a camera or image sensor is likely to be exposed to sunlight for long periods of time include automotive headlight control systems such as that disclosed in commonly assigned U.S. patent application Ser. No. 09/528,389, entitled “IMPROVED VEHICLE LAMP CONTROL,” and filed on Mar. 20, 2000; automotive moisture sensing systems such as that disclosed in commonly-assigned U.S. Pat. No. 5,923,027; and in automotive electronic vision systems such as those disclosed in commonly-assigned U.S. patent application Ser. No. 09/001,855, entitled “VEHICLE VISION SYSTEM,” and filed on Dec. 31, 1997, and commonly-assigned U.S. patent application Ser. No. 09/153,654, entitled “SYSTEMS AND COMPONENTS FOR ENHANCING REAR VISION FROM A VEHICLE,” and filed on Sep. 15, 1998. The disclosures of the above-noted patent and patent applications are incorporated herein by reference.
Mechanical and electromechanical shutters, when used, are not typically part of the optical sensor package. Electrically attenuated grayscale filters are never part of the commercial sensor device package, if available at all.
What is needed is a package for protecting an optical sensor that is inexpensive, compact, and easy to manufacture. The package should be adaptable to include an electronically controlled electrochromic variable attenuator.